Retroreflective sheeting containing a validation image and methods of making the same

ABSTRACT

This invention relates to retroreflective sheeting which has an image, such as an image. More specifically, the image has varying appearance at different angles of view. The retroreflective sheeting has a layer of transparent microsphere lenses, a transparent polymeric spacing layer underlying, contacting, and conforming to the bottom of the lenses, the spacing and conformation of which is critical to the optimal performance of the retroreflective article, a reflective layer having a top surface in contact with the back surface of the spacing layer and a topcoat and/or cover sheet overlying and conforming to the top surfaces of the lenses and having a flat top surface or face. In another embodiment, the retroreflective sheeting includes a pressure sensitive adhesive underlying and in contact with the reflective layer. The retroreflective sheeting has an image whose proportions are determined by a non-conformity of the reflective and spacing layer to the bottom of the lenses. The image of the present invention can range from conspicuous to inconspicuous and directional to non-directional.

CROSS REFERENCE TO PROVISIONAL APPLICATION

[0001] This application claims priority from provisional applicationSer. No. 60/106,359, filed Oct. 30, 1998, the entire disclosure of whichis hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to a retroreflective sheeting withan image, more specifically a validation image.

BACKGROUND OF THE INVENTION

[0003] Validation images have been used for years for authentication andsecurity purposes. A watermark is an identifying pattern or legendeither on or in a material to provide validation of the material.Retroreflective sheeting with directional and non-directional watermarkshave been used as a validation means for documents, phonographs,cassette tapes, compact disk containers, traffic signage and licenseplates.

[0004] One problem with watermarks on retroreflective material isproviding the watermark in a manner which provides the neededauthentication but which provides some subtlety or inconspiciousness,such as being discernable in only a few angles of viewing. Oftenexpensive processing steps and equipment are required to provide such awatermark. Additionally, there is generally little processing controlover the conspiciousness or intensity of the watermark.

[0005] It is desirable to have an image which is distinct and viewablefor authenticating purposes. Further, it is desirable to have aprocessing means to provide the desired intensity of the image. Finally,it is also desirable to have an image which may be subtle anddirectional.

SUMMARY OF THE INVENTION

[0006] This invention relates to retroreflective sheeting which has animage, such as a validation image. In one embodiment, the image isdirectional having varying appearance at different angles of view. Theretroreflective sheeting has a layer of transparent microsphere lenses,a transparent polymeric spacing layer underlying, contacting, andconforming to the bottom of the lenses, the spacing and conformation ofwhich is critical to the optimal performance of the retroreflectivearticle, a reflective layer having a top surface in contact with theback surface of the spacing layer and a topcoat and/or cover sheetoverlying and conforming to the top surfaces of the lenses and having aflat top surface or face. In another embodiment, the retroreflectivesheeting includes a pressure sensitive or thermally activated adhesiveunderlying and in contact with the reflective layer. The retroreflectivesheeting has an image whose proportions are determined by anon-conformity of the reflective and spacing layer to the bottom of thelenses. The image of the present invention can range from conspicuous toinconspicuous and directional to non-directional.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a cross sectional view of a retroreflective sheeting.

[0008]FIG. 2 is a cross sectional view of a retroreflective sheeting.

[0009]FIG. 3 is a cross sectional view of a retroreflective sheeting.

[0010]FIG. 4 is an illustration of the method of imparting the image.

[0011]FIG. 5 is an illustration of an alternative method of impartingthe image.

[0012]FIG. 6 is an illustration of an another alternative method ofimparting the image.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] As described herein, the invention relates to a retroreflectivesheeting which has an image. The image is a portion of the reflectivelayer which does not conform, or is less conforming to the back surfaceof the microsphere lenses. The portion of the reflective layer, which isout of conformity, does not provide the same magnitude ofretroreflectivity as the conforming areas. This non-conforming area canrange from a “dead” or nonreflecting, to a less reflecting portion, to agreater reflecting portion of the retroreflective sheeting. Thisdifference in reflective characteristic leads to the image'sviewability. The apparent intensity of the image is related to thedegree of non-conformity of the spacing and/or the reflective layers.

[0014] As described above the retroreflective sheeting has a layer oftransparent microsphere lenses. The microsphere lenses may have anyrefractive index or average diameter provided that the beads provide thenecessary refraction for the retroreflective application. Typically themicrosphere lenses are characterized as having an average refractiveindex in the range of about 1.8 to about 2.5, or from about 1.9 to about2.4, or from about 2.1 to about 2.3 and an average diameter of about 35to about 100, or from about 45 to about 90, or from about 55 to about 80microns. Here and elsewhere in the specification and claims the rangeand ratio limits may be combined. The transparent microsphere lensesutilized in the retroreflective sheeting of the present invention may becharacterized as having average diameters in a range of from about 25 toabout 300, 30 to about 120 microns, and more often in a range from about40 to about 80 microns. The index of refraction of the microspherelenses is generally in the range from about 1.9 to about 2.5, moretypically is in the range from about 2.0 to about 2.3, and most oftenbetween about 2.10 to about 2.2.

[0015] Glass microspheres are typically used although ceramicmicrospheres such as those made by sol/gel techniques can also be used.The index of refraction and the average diameter of the microspheres,and the index of refraction of the topcoat and/or cover sheet and spacecoat dictate the thickness of the spacing film. The microspheres can besubjected to chemical or physical treatments to improve the bond of themicrospheres to the polymeric films. For example, the microspheres canbe treated with a fluorocarbon or an adhesion promoting agent such as anaminosilane to improve the bond, or the space coat layer in which thelenses have been embedded can be subjected to a flame treatment orcorona discharge to improve the bond between the space coat and lensesto the subsequently applied topcoat and or cover sheet.

[0016] The retroreflective sheeting also has a spacing layer generallyconforming to the bottom surface of the microsphere lenses. Thethickness of the polymeric spacing layer or space coat is from about 25%to about 100%, or from 40% to about 60% of the average diameter of themicrosphere lenses. Various thermoplastic polymeric resins have beenused previously in forming the spacing layer of embedded lensretroreflective sheeting, and such resins can be used in the sheeting ofthe present invention. The resins that may be used for the spacing layerinclude a variety of partially amorphous or semi-crystallinethermoplastic polymers which generally have a soft stage during whichthe lenses can be embedded in the films. The material used to form thespacing film or layer should be compatible with the topcoat material andadapted to form a good bond with the topcoat (and the microspherelenses). Preferably, the adhesion between the materials is greater thanthe tensile strength of the materials. Acrylics, polyvinyl butyrals,aliphatic urethanes and polyesters are particularly useful polymermaterials because of their outdoor stability. Copolymers of ethylene andan acrylic acid or methacrylic acid; vinyls, fluoropolymers,polyethylenes, cellulose acetate butyrate, polycarbonates andpolyacrylates are other examples of polymers that can be used for thetopcoat and spacing layers of the sheeting of the invention. In oneembodiment it is desirable to use materials having elastomericproperties to provide retroreflective sheeting which may be repeatedlystretched or flexed, and upon release of the stretching or flexingtension, rapidly return to substantially their original dimensionswithout significant loss of retroreflectivity. Polyurethanes areavailable which possess such elastomeric properties and these materialscan be used as space coat materials.

[0017] In another embodiment it is desirable to use two or more layersto form a topcoat/cover sheet layer. These may consist of any of theaforementioned materials in combination with a transparent pressuresensitive adhesive (such as AS352RX acrylic adhesive from Avery Chemicalin Mill Hall Penn.) underlying the cover sheet and in intimate contactand conforming to the microspheres. The cover sheet or pressuresensitive adhesive can be colored with a transparent pigment or dye oreven be printed with a graphic which can be located on the interior orthe exterior of the cover sheet. In yet another embodiment the pressuresensitive adhesive can be replaced by a thermal bonding layer, a heatactivated adhesive, or a material which forms chemical bonds to thecover sheet.

[0018] The retroreflective sheeting has a topcoat or cover sheetoverlying and conforming to the top surface of the microsphere lenses.The coating weight of the topcoat may range from about 25 to 175 gms/m².Preferably the coating weight is about 50 to 150 gms/m² and morepreferably is from about 60 to 120 gms/m². The topcoat thickness mayrange from 25 to about 125 microns and more often is from about 50-100microns.

[0019] The cover may comprise various thermoplastic polymers includingacrylic polymer such as polymethylmethacrylate, vinyl polymers such asPVC and vinyl acrylic copolymers, or polyurethanes such as aliphaticpolyether urethanes. Cover sheets include an impact modifiedpolymethylmethacrylate (PMMA) (e.g., Plexiglas™ acrylic DR, MI-7 (Rohm &Haas), Perspex™ acrylic HI-7 (ICI), or blends thereof), a vinyl acrylicformulation (methyl methacrylate/butyl methacrylate) copolymer and a PVChomopolymer) or a polyurethane. The aliphatic polyurethane cover sheetis produced by casting the urethane onto a polymer coated paper castingsheet or onto a polymer casting sheet. Casting sheet products are wellknown to the industry and supplied by companies such as Felix SchoellerTechnical Papers, Pulaski, N.Y., S. D. Warren of Newton Center, Mass.and Ivex Corporation of Troy, Ohio. The urethane coating is coated ontothe casting sheet by standard coating methods such as curtain coating,slot die coating, reverse roll coating, knife over roll coating, airknife coating, gravure coating, reverse gravure coating, offset gravurecoating, Meyer rod coating, etc. To achieve proper performance and coatweight thickness in each of the coating operations, technical expertiseis applied to determine the optimal urethane solution viscosity. Theapplication of these coating techniques is well known in the industryand can effectively be implemented by one skilled in the art. Theknowledge and expertise of the manufacturing facility applying thecoating determine the preferred method. Further information on coatingmethods can be found in “Modern Coating and Drying Technology”, byEdward Cohen and Edgar Gutoff, VCH Publishers, Inc., 1992. Extrusion orextrusion coating are alternate methods of forming a urethane film.

[0020] The retroreflective sheeting may also include a pressuresensitive adhesive and optionally a release liner. For example, anadhesive layer can be applied over the reflective layer to protect thereflective layer and to serve a functional purpose such as adhering thesheeting to a substrate. Conventional pressure-sensitive adhesives suchas acrylic-based adhesives, or heat- or solvent-activated adhesives aretypically used and may be applied by conventional procedures. Forexample, a preformed layer of adhesive on a carrier web or release linercan be laminated to the reflective layer. Conventional release linerscan be utilized in the formation of the retroreflective sheeting of thepresent invention.

[0021] The retroreflective sheeting is further illustrated in referenceto the drawings. In FIG. 1, retroreflective sheeting 10 has a coversheet, e.g. a polyurethane 11, in which are embedded glass microspheres12. The glass microspheres are also adhered to spacecoat, e.g.polyvinylbutyral, 13. Reflecting surface (vapor deposited aluminum) 14is attached to spacecoat 13. A pressure sensitive adhesive 15 andrelease liner 16 are adhered to reflecting surface 14. Images 17 and 18are portions of the reflective and spacecoat layers which arenon-conforming to the glass beads 12.

[0022]FIG. 2 illustrates a retroreflective sheeting which does not havea pressure sensitive adhesive. Retroreflective sheeting 20 has coversheet 21 attached to glass microspheres 22, which are also attached tospacecoat 23. A reflecting surface 24 is on spacecoat 23. Images 25 and26 are non-conforming sections of the reflective and spacecoat layers 23and 24.

[0023]FIG. 3 illustrates a retroreflective sheeting which has amultilayer covering. Retroreflective sheet 30 which has cover sheet 31which is adhered to pressure sensitive adhesive 32. Adhesive 32 isbonded to glass microspheres 33, which are also attached to spacecoat34. A reflecting surface 35 is on spacecoat 34. The reflecting surface35 is adhered to pressure sensitive adhesive 36 which is also releasablyadhered to release liner 37. The retroreflective sheeting has images 38and 39.

[0024] The images of the present invention may be prepared by usingembossing or flexographic printing techniques. The images may beprepared by pressing a pattern into the retroreflective sheeting at thepressure and temperature necessary to provide the desired image.

[0025] The retroreflective sheeting can be made by procedures normallyused in the industry. For example, the sheeting of the invention can beprepared by first extruding or casting a space coat layer of desiredthickness on a polymer coated casting sheet and drying if necessary. Thespace coat layer is reheated to provide a tacky surface upon whichmicrospheres are cascade-coated to form a monolayer of the microspheres.Typically, heat and/or pressure can be applied at this stage tofacilitate microsphere embedding. The microspheres generally areembedded into the layer to a depth of about one-half of the averagediameter of the microspheres. It is important that the space coat adaptsa contour parallel to the microsphere surface. The topcoat is thenapplied over the top of the exposed and partially embedded microspheres.

[0026] The topcoating is applied by standard coating methods such asthose described above. It is also possible to cast the topcoat as aseparate, single layer film using these coating techniques. To achieveproper performance and coat weight thickness in each of the coatingoperations, technical expertise must be applied to determine the optimalsolution viscosity. The application of these coating techniques is wellknown and is described above. Extrusion or extrusion coating arealternate methods of forming a topcoat. If required, the topcoat and thebase coat layer are then subjected to an elevated temperature to dry orcure.

[0027] The polymer coated casting sheet then is stripped from the spacecoat layer, and a reflective layer is subsequently applied over the backsurface of the space coat. For example, a reflective layer of silver oraluminum metal can be applied by vapor deposition over the back surfaceof the space coat. The thickness of the reflective layer depends on theparticular metal used and is generally between about 500 and 1000nanometers. The topcoat layer then can be printed (e.g. with UVradiation curable inks) to provide monocolor or multicolor images withthe optional transparent overcoat.

[0028] An alternate manufacturing process for enclosed bead-typeretroreflective products can be used by first applying a polyurethanemixture onto a casting sheet and exposing the newly cast film to heatfor solvent evaporation and urethane curing. After the film is formed, abead bonding layer is applied and typically exposed to elevatedtemperatures for curing and/or evaporation of a carrier vehicle, such assolvent. Though many materials may be used for the bead bond layer, athermoplastic polymer is preferred. The bead bond layer can then bepartially cured or re-softened by the application of heat to allowcascade coated microspheres to form a monolayer of microspheres. Themicrospheres generally are embedded into the bead bond layer in aprocess that uses the application of heat and/or pressure. The spacecoat layer of desired thickness is then applied over the exposedmicrospheres. Next, the space coat and base coat layers are subjected toelevated temperatures to complete solvent drying and/or curing and toprovide adequate conformation of the spacecoat to the microspheresurface.

[0029] As described above, a reflective layer is subsequently appliedover the back surface of the space coat layer. After the originalcasting sheet is stripped from the product, the top aliphaticpolyurethane layer can be printed (e.g. with UV radiation curable inks)to provide monocolor or multicolor images with the optional transparentovercoat or overlaminate film.

[0030] In another embodiment, the retroreflective sheeting described ina previous paragraph is provided with a pressure-sensitive adhesiveconstruction. In this embodiment, a pressure-sensitive adhesive iscoated onto a release coated liner (paper or polymer) thereafter theadhesive coated liner is pressure laminated to the exposed surface ofthe reflective layer. This embodiment is illustrated in FIG. 1. Therelease coated liner can subsequently be removed and the retroreflectivesheeting can be adhesively applied to other surfaces.

[0031] The validation image has at least one portion which isnon-conforming to the lenses. In one embodiment, the image is preparedby pressing the image design into the reflective surface of theretroreflective sheeting. The reflective layer of retroreflectivesheeting is forced against a heated roll, such as a heated steel roll,by another roll, such as a rubber embossing or a flexo printing roll,containing the design of the image. The pressure and temperature as wellas the speed of the roll affect the flattening of the crowns of thereflective layer. The pressure is typically from about 5 to about 75, orfrom about 10 to about 35, or from about 15 to about 25 pounds perlinear inch (pli). The temperature of the heated roll is from about 85to about 130, or from about 90 to about 120, or from about 95 to about110 degrees C. The speed of the roll is typically from about 5 to about100, or from about 8 to about 80, or from about 10 to about 60 ft/min.In one embodiment, the mechanical stops on the embossing andflexographic printing equipment are set to control the depth of theimpression of the image. The mechanical stops are set so that the rollwith the image design is not forced onto the heated roll when betweenthe raised image designs. The roll with the image design then justtouches or kisses the surface of the retroreflective sheeting, thusforming the image.

[0032]FIG. 4 illustrates the method of imparting the image. Heated steelroll 41 contacts the reflective side of retroreflective sheeting 42. Thetopcoat side of sheeting 42 is pressed against flexographic roll 43bearing the raised impression 44 of the desired image. After beingsubjected to the heating and pressing step, the sheeting 42 has images.

[0033] The roll used for the image design may be any roll used forembossing or flexo printing. The advantage of the present process isthat the relatively inexpensive equipment may be used for preparing theretroreflective sheeting with the image. With the use of the heated rollthe present process provides a simple means to prepare a retroreflectivesheeting with an image.

[0034] An alternative method of imparting an image can be made by firstembossing an image into the face of the polymer coated surface of acasting sheet. This can easily be done into thermoplastic materialsusing the techniques for embossing holographic images. For example, thesheeting of the invention can be prepared by first extruding or castinga space coat layer of desired thickness on an imaged polymer coatedcasting sheet and drying if necessary. The space coat layer is reheatedto provide a tacky surface upon which microspheres are cascade-coated toform a monolayer of the microspheres. Typically, heat and/or pressurecan be applied at this stage to facilitate microsphere embedding. Themicrospheres generally are embedded into the layer to a depth of aboutone-half of the average diameter of the microspheres. It is importantthat the space coat adapts a contour parallel to the microsphere surfaceand that the image substantially remains intact. The topcoat is thenapplied over the top of the exposed and partially embedded microspheres.

[0035] The topcoating is applied by standard coating methods asdescribed above. Extrusion can be considered as an alternate method offorming a topcoat. If required, the topcoat is then subjected to anelevated temperature to dry and/or cure the mixture.

[0036] The polymer coated casting sheet then is stripped from the imagedspace coat layer, and a reflective layer is subsequently applied overthe back surface of the space coat as described above. The topcoat layerthen can be printed as described above.

[0037]FIG. 5 illustrates an alternative method of imparting the image.In FIG. 5a, article 50 has a substrate 51 which is adhered to polymerfilm (e.g. polyethylene) 52. Heat and pressure are used to emboss animage 53, such as a holographic image into the surface of a polymer film52. In FIG. 5b, spacecoat (e.g. polyvinylbutyral) 54 is coated on topolymer film 52. The image 53 in polymer 52 is replicated in the bottomsurface of spacecoat 54. In FIG. 5c, glass microspheres 55 are embeddedinto spacecoat 54, the spacecoat is molded by the polymer layer 52 to acontour parallel to the microsphere surface and the image substantiallyremains intact. In FIG. 5d, a topcoat 56 is coated on the exposedsurface of the glass microspheres 55. In FIG. 5e, the substrate 51 andpolymer film 52 are removed from the construction. The spacecoat 54 withholographic images 53 is metallized as described above to form areflective layer 57.

[0038] Another alternative method of imparting an image can be made byfirst printing an image using a transparent polymer or a transparentlycolored polymer onto the face of the polymer coated surface of a castingsheet. The printing can be done using common printing techniques such asFlexography (flexo) and Rotogravure (gravure). Heat and pressure areused to press the image into the face of the polymer coated substrate sothat the top of the print is substantially level with the polymer coatedsurface. For example, the sheeting of the invention can be prepared byfirst extruding or casting a space coat layer of desired thickness on animaged polymer coated casting sheet and drying if necessary. The spacecoat layer is reheated to provide a tacky surface upon whichmicrospheres are cascadecoated to form a monolayer of the microspheres.Typically, heat and/or pressure can be applied at this stage tofacilitate microsphere embedding. The microspheres generally areembedded into the layer to a depth of about one-half of the averagediameter of the microspheres. It is important that the space coat adaptsa contour parallel to the microsphere surface and that the imagesubstantially remains intact. The topcoat is then applied over the topof the exposed and partially embedded microspheres.

[0039] The topcoating is applied by standard coating methods asdescribed above. Extrusion can be considered as an alternate method offorming a topcoat. If required, the topcoat and the base coat layer arethen subjected to an elevated temperature to dry or cure.

[0040] The polymer coated casting sheet then is stripped from the imagedspace coat layer, and a reflective layer is subsequently applied overthe back surface of the space coat as described above. The printed imageis non-conforming with the microspheres. The topcoat layer then can beprinted (e.g. with UV radiation curable inks) to provide monocolor ormulticolor images.

[0041]FIG. 6 illustrates an alternative method of imparting the image.In FIG. 6a, article 60 has a substrate (e.g. paper) 61 which is adheredto polymer film (e.g. polyethylene) 62. An image is printed using atransparent or transparently colored polymer (e.g. polyvinylbutyral) onthe surface of polymer 62. In FIG. 6b, the image 63 is embedded intopolymer layer 62 using heat and pressure. In FIG. 6c, spacecoat (e.g.polyvinylbutyral) 64 is coated onto the surface of polymer film 62containing embedded images 63. In FIG. 6d, glass microspheres 65 areembedded into spacecoat 64, the spacecoat is molded by the polymer layer62 to a contour parallel to the microsphere surface and the imagesubstantially remains intact. In FIG. 6e, a topcoat (e.g. aliphaticpolyurethane) 66 is coated on the exposed surface of the glassmicrospheres 65. In FIG. 6f, the substrate 61 and polymer film 62 areremoved from the construction. The spacecoat 64 with images 63 ismetallized as described above to form a reflective layer 67.

[0042] While the invention has been explained in relation to itspreferred embodiments, it is to be understood that various modificationsthereof will become apparent to those skilled in the art upon readingthe specification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

1. A retroreflective sheet with an image comprising a layer oftransparent microsphere lenses, a transparent polymeric spacing layercontacting and conforming to the bottom of the lenses wherein thespacing layer has at least one portion which is non-conforming to thelenses, a reflective layer having a top surface in contact with the backsurface of the spacing layer and a topcoat and/or cover sheet overlyingand conforming to the top surfaces of the lenses and having a flat topsurface or face wherein the non-conforming portion of the spacing layerforms the image.
 2. The retroreflective sheet of claim 1 wherein themicrospheres have an average refractive index in the range of about 1.8to about 2.5.
 3. The retroreflective sheeting of claim 1 wherein themicrospheres are glass microspheres with a average diameters in a rangeof from about 25 to about 300 microns.
 4. The retroreflective sheet ofclaim 1 wherein the spacing layer is an acrylic polymer, a polyvinylbutyral, an aliphatic urethane and a polyester.
 5. The retroreflectivesheet of claim 1 wherein the spacing layer is polyvinylbutyral.
 6. Theretroreflective sheet of claim 1 wherein the coating thickness of thepolymeric spacing layer is from about 25% to about 100% the averagediameter of the microsphere lenses.
 7. The retroreflective sheet ofclaim 1 wherein the topcoat has a thickness from about 25 microns toabout 300 microns.
 8. The retroreflective sheet of claim 1 wherein thetopcoat is derived from at least one acrylic polymer, a vinyl polymer,or polyurethanes.
 9. The retroreflective sheet of claim 1 wherein thesheet includes a topcoat and a cover sheet.
 10. The retroreflectivesheet of claim 9 wherein the topcoat is a pressure sensitive adhesiveand the cover sheet is derived from at least one acrylic polymer, avinyl polymer, or polyurethanes.
 11. The retroreflective sheet of claim9 wherein the topcoat is a partially cured urethane and the cover sheetis derived from at least one acrylic polymer, a vinyl polymer, orpolyurethanes.
 12. The retroreflective sheet of claim 9 wherein thetopcoat is a heat activated adhesive and the cover sheet is derived fromat least one acrylic polymer, a vinyl polymer, or polyurethanes.
 13. Theretroreflective sheet of claim 1 further comprising a pressure sensitiveadhesive underlying and in contact with the reflective layer.
 14. Aretroreflective sheet with an image comprising a monolayer oftransparent glass microsphere lenses, a polyvinylbutyral transparentpolymeric spacing layer contacting and conforming to the bottom of thelenses, a reflective layer having a top surface in contact with the backsurface of the spacing layer and a polyurethane topcoat and/or coversheet overlying and conforming to the top surfaces of the lenses andhaving a flat top surface or face wherein the image is a non-conformingportion of the spacing layer and the reflective layer.
 15. Theretroreflective sheet of claim 14 wherein the microspheres have anaverage refractive index in the range of about 2.0 to about 2.3.
 16. Theretroreflective sheeting of claim 14 wherein the microspheres are glassmicrospheres with a average diameters in a range of from about 30 toabout 120 microns.
 17. The retroreflective sheet of claim 14 wherein thecoating thickness of the polymeric spacing layer or space coat is fromabout 35% to about 75% of the average diameter of the microspherelenses.
 18. The retroreflective sheet of claim 14 wherein the topcoathas a thickness from about 25microns to about 125 microns.
 19. Theretroreflective sheet of claim 14 further comprising a pressuresensitive adhesive underlying and in contact with the reflective layer.20. A method of preparing a retroreflective sheet with an imagecomprising the steps of (1) providing retroreflective sheeting having aspacing and reflective layer conforming to glass lenses, (2) heating theretroreflective sheeting and (3) pressing an image onto the spacinglayer of the retroreflective sheet to form an image which isnon-conforming to the lenses.
 21. The method of claim 20 wherein thepressure is from about 5 to about 75 pounds per linear inch.
 22. Themethod of claim 20 wherein the retroreflective sheet is heated to about85 to about 130 degrees C.
 23. A method of making a retroreflectivesheet with an image comprising the following steps: (1) pressing animage into a molding layer surface of a first assembly which comprises amolding layer and a substrate, (2) coating a transparent polymericspacing layer on the imaged surface of the molding layer, (3) depositinga monolayer of transparent microsphere lenses onto the transparentpolymeric spacing layer, (4) embedding by means of heat and pressure themonolayer of microsphere lenses into the transparent polymeric spacinglayer which adheres to and conforms to the bottom surface of themonolayer of transparent microsphere lenses displacing the molding layerbut substantially keeping the image intact, (5) covering the exposedtransparent microsphere lenses with a transparent topcoat and/ortransparent cover sheet, (6) removing the molding layer and substrateassembly, and (7) depositing a reflective layer over the exposed surfaceof the transparent polymeric spacing layer.
 24. A method of claim 23 inwhich the Vicat softening point of the molding layer is less than thatof the transparent polymeric spacing layer.
 25. A method of claim 23wherein the molding layer comprises a low, medium, or high densitypolyolefin.
 26. A method of claim 23 further comprising a siliconerelease layer between the transparent polymeric spacing layer and themolding layer.
 27. A method of claim 23 in which the image is aholographic image embossed into the molding layer.
 28. A method ofmaking a retroreflective sheet with an image comprising the followingsteps: (1) printing an image using a transparent or transparentlycolored polymer onto a molding layer surface of a first assembly whichcomprises a molding layer and a substrate, (2) pressing the printedimage into a molding layer surface of a first assembly which comprises amolding layer and a substrate, (3) coating a transparent polymericspacing layer on the imaged surface of the molding layer, (4) depositinga monolayer of transparent microsphere lenses onto the transparentpolymeric spacing layer, (5) embedding by means of heat and pressure themonolayer of microsphere lenses into the transparent polymeric spacinglayer which adheres to and conforms to the bottom surface of themonolayer of transparent microsphere lenses displacing the molding layerbut substantially keeping the image intact, (6) covering the exposedtransparent microsphere lenses with a transparent topcoat and/ortransparent cover sheet, (7) removing the molding layer and substrateassembly, and (8) depositing a reflective layer over the exposed surfaceof the transparent polymeric spacing layer.
 29. A method of claim 28 inwhich the Vicat softening point of the molding layer is less than thatof the transparent polymeric spacing layer.
 30. A method of claim 28wherein the molding layer comprises a low, medium, or high densitypolyolefin.
 31. A method of claim 28 further comprising a siliconerelease layer between the transparent polymeric spacing layer and themolding layer.